The Quantitative Core provides leadership, consultation, support services, and training to CAIR investigators and scientific personnel in the areas of data management, biostatistics, research design, and data analysis. In addition, the Core provides leadership in the conduct of assessment methodology research and the design of data collection instruments, and interacts with other CAIR Cores in matters related to quantitative models, design, and analysis. Quantitative Core Scientists develop, supervise the entry process, manage, and maintain program-wide research databases. Core Scientists perform these activities in a variety of ways including through the Core's facility and using procedures for the centralized entry and management of research data; consultation to individual CAIR investigators and project investigation teams; participation in Center scientific planning and decision making; and participation in CAIR Conferences, research seminars, and research training. The evaluation of HIV prevention interventions requires reliable and valid assessment techniques, the collection and management of large volumes of data, and the use of sophisticated and appropriate statistical tools for evaluating the impact of an intervention in complex studies conducted in real-world settings. Statistical methods play a crucial role in determining the uncertainty associated with the impact of these interventions. The Core provides leadership in the development and evaluation of assessment measures and the design of data collection instruments. Accepted standards in the entry, management, and screening of research data are recognized as key steps in the scientific analysis of research. Through the creation of a Center-wide data management facility and standard procedures for data handling, the Core has achieved uniformity in the management of research data collected in CAIR studies. A number of features of HIV prevention interventions--including the complexity of community intervention and the complexity of sexual behavioral practice patterns-- influence the proper development of statistical models for assessing intervention impact. Bringing statistical issues and findings reported in the statistical literature to bear when relevant on study development, design, and analysis is both an important Core scientific contribution. In addition, the Quantitative Core works in conjunction with other Cores to operate in a synergistic functional relationship. This relationship enables the Quantitative Core to benefit the functions of the other Cores, while also benefiting from the expertise available in them.